Danfoss VLT AutomationDrive FC 300 Programming Manual page 138

Parameter Descriptions
14-10 Mains Failure
Option:
3 3
[0] No
function
[1] Ctrl.
ramp-
down
[2] Ctrl.
ramp-
down,
trip
[3] Coasting
[4] Kinetic
back-up
136
Function:
interruption, the DC voltage on the main
capacitors drops quickly. For larger drives it only
takes a few milliseconds before the DC level is
down to about 373 V DC and the IGBTs cut off
and looses the control over the motor. When the
mains is restored, and the IGBTs start again, the
output frequency and voltage vector does not
correspond to the speed/frequency of the motor,
and the result is normally an overvoltage or
overcurrent, mostly resulting in a trip lock.
14-10 Mains Failure can be programmed to avoid
this situation.
Select the function to which the frequency
converter must act when the threshold in
14-11 Mains Voltage at Mains Fault has been
reached.
14-10 Mains Failure cannot be changed while
motor is running.
The frequency converter will not compensate for a
mains interruption. The voltage on the DC-link will
drop quickly and motor control will be lost within
milliseconds to seconds. Trip lock will be the
result.
The frequency converter will remain control of the
motor and do a controlled ramp down from
14-11 Mains Voltage at Mains Fault level. If
2-10 Brake Function is [0] Off or [2] AC brake, the
ramp will follow the Over Voltage Ramping. If
2-10 Brake Function is [1] Resistor Brake the ramp
will follow the setting in 3-81 Quick Stop Ramp
Time. This selection is particularly useful in pump
applications, where the inertia is low and the
friction is high. When the mains is restored, the
output frequency will ramp the motor up to the
reference speed (if the mains interruption is
prolonged, the controlled ramp down might take
the output frequency all the way down to 0 RPM,
and when the mains is restored, the application is
ramped up from 0rpm to the previous reference
speed via the normal ramp up). If the energy in
the DC-link disappears before the motor is ramped
to zero the motor will be coasted.
This selection is similar to selection [1] except that
in [2] a reset is necessary for starting up after
power-up.
Centrifuges can run for an hour without power
supply. In those situations it is possible to select a
coast function at mains interruption, together with
a flying start which occurs when the mains is
restored.
Kinetic back-up ensures that the frequency
converter keeps running as long as there is energy
MG33MG02 - VLT
®
VLT AutomationDrive Programming Guide
14-10 Mains Failure
Option:
®
is a registered Danfoss trademark
Function:
in the system due to the inertia from motor and
load. This is done by converting the mechanical
energy to the DC-link and thereby maintaining
control of the drive and motor. This can extend
the controlled operation, depending on the inertia
in the system. For fans it is typically several
seconds, for pumps up to 2 seconds and for
compressors only for a fraction of a second. Many
industry applications can extend controlled
operation for many seconds, which is often
enough time for the mains to return.
A B C D E
U [V]
DC
U DC
14-11*1.35
n [RPM]
Ref
Illustration 3.54 Kinetick Back-up
A Normal operation
B Mains failure
C Kinetic back-up
D Mains return
E Normal Operation: ramping
Table 3.23 Legend to Illustration 3.54
The DC-level during [4] Kinetic back-up is
14-11 Mains Voltage at Mains Fault * 1.35.
If the mains do not return U is maintained as
DC
long as possible by ramping the speed down
towards 0 RPM. Finally the frequency converter
coasts.
If the mains return while in kinetic back-up U
will increase above 14-11 Mains Voltage at Mains
Fault*1.35. This is detected in one of the following
ways.
1. If U > 14-11 Mains Voltage at Mains
DC
Fault*1.35*1.05
2. If the speed is above the reference. This
is relevant if the mains come back at a
lower level than before, e.g. 14-11 Mains
Voltage at Mains Fault*1.35*1.02. This
does not fulfil the criterion in point one
and the frequency converter will try to
reduce U to 14-11 Mains Voltage at
DC
Mains Fault*1.35 by increasing the speed.
This will not succeed as the mains
cannot be lowered.
A
t [S]
t [S]
DC